Numerically controlled turret lathes and turning centers generally comprise a motor-driven spindle having a chuck or faceplate for clamping or attaching a workpiece such that the workpiece rotates with the spindle. Opposite the spindle is a turret having a plurality of index positions angularly spaced about a pivot axis of the turret. Each index position may be allocated a different tool for engaging the workpiece. The turret is automatically indexable to bring a desired tool into a working position for engaging the workpiece, such that a programmed sequence of different machining operations may be performed on the workpiece without need for operator intervention.
The tools carried on the turret may include, for example, drill bits, reamers, boring tools, turning tools, facing tools, thread forming tools, and grooving tools. Some of these tools, such as a turning and boring tools, are typically mounted at the end of a rectangular bar, whereas others such as drill bits and reamers are formed at the end of a cylindrical shank. The rectangular bar or cylindrical shank, as the case may be, is gripped by a tool holder mounted on the turret or provided as an integral part of the turret. As used herein, the term “shank” in reference to a tool means both a rectangular bar and a cylindrical shank. One common type of tool holder is a VDI tool holder, which follows standards established by the Association of German Engineers in the early 1970s. These tool holders are characterized by a jagged toothed shaft adapted to be gripped by a VDI chucking mechanism.
A recognized drawback of tool change turrets is that a single tool is allocated to each index position of the turret, such that the turret must be indexed to select a different tool if called for by the programmed sequence of machining operations. Although indexing is carried out automatically in accordance with the machining program, it adds to the overall run time required to machine the workpiece into a finished part. While the additional time for indexing may be a small portion of the overall run time for a single part, the additional time accumulates and becomes quite significant in the context of a production job where a very large number of parts is produced.
Currently, applicants are aware of three commercial products intended to allow more than one tool to be allocated to a single turret index position, thereby making it possible to avoid turret indexing time for some tool changes. The first product is marketed under the trademark TURRETGANG, and includes a rectangular bar shank for mounting at an OD tool index position of a turret. A tool block portion is provided at a distal end of the rectangular bar shank and includes three cylindrical tool-receiving openings spaced along an X-axis of the CNC machine for holding three inner diameter (“ID”) tools. The tool block portion also includes coolant passages.
The second product is marketed under the trademark TRIPLIT, and includes a cylindrical shank for mounting in a round drill index position of a turret. The TRIPLET includes a tool block portion coaxially arranged at a distal end of the shank. The tool block portion has three cylindrical tool-receiving openings spaced along an X-axis of the CNC machine for holding three ID tools. The tool block portion also includes coolant passages.
The third product known to applicant is a line of multi-tool blocks offered by Engbar Inc. of Las Vegas, Nev. having multiple cylindrical tool-receiving openings for holding a plurality of ID tools.
One drawback of the existing tooling block products is that they are relatively heavy, which can lead to inaccuracies in positioning a given tool relative to the lather spindle when the turret is indexed. To reduce inaccuracies to acceptable tolerance levels, the number of tools carried by the tooling block must be limited.
Another drawback of the existing tooling block products is that both ID and OD tools cannot be allocated to the same index position on a turret.